Paying Roth Conversion Taxes From Your IRA: The Costly Mistake
Key Takeaways
- Withholding the tax out of the IRA means those dollars never reach the Roth, so the conversion you paid for is smaller than the one you intended.
- Paying the tax from cash or a taxable account lets the entire converted amount land in the Roth, where future growth isn't taxed under current rules.
- If you're under 59 and a half, the amount withheld for taxes is generally treated as a distribution rather than a conversion, which can add a 10% early distribution penalty on top of the income tax.
- Not having outside cash is a reason to convert less this year, not a reason to withhold from the account.
- A conversion itself can't be reversed, but if tax was withheld you generally have 60 days to replace the withheld dollars from outside funds and roll the full amount into the Roth.
Most of the attention around a Roth conversion goes to the decision itself: whether to convert, and how much. Far less goes to a question usually answered almost by accident on the custodian's form: where the money to pay the tax bill comes from.
You can have the custodian withhold the tax out of the IRA as part of the conversion, which is the path of least resistance. Or you can convert the full amount and pay the tax from cash you hold outside the retirement account.
Same conversion, very different Roth balance. The difference doesn't show up on this year's tax return. It shows up decades later.
In this guide, you'll see:
- Why the tax funding source is its own decision, separate from the conversion amount
- What withholding from the conversion actually costs you
- Why withholding adds a penalty if you're under 59 and a half
- How to fund the tax bill without shrinking the conversion
Table of Contents
Where the Tax Money Comes From Is Its Own Decision
A Roth conversion moves pretax dollars from a traditional IRA or 401(k) into a Roth account and adds the converted amount to your ordinary income for that year, assuming you have no after-tax basis in your traditional IRAs.
Where nondeductible contributions exist, the pro-rata rule under Internal Revenue Code section 408(d)(2), reported on Form 8606, makes only part of it taxable. Either way the tax is owed. What changes is which dollars pay it.
Cash in a checking or taxable brokerage account is already taxed on its earnings every year; dollars inside the IRA are not. Withhold from the IRA and you spend the better-treated account to settle a bill ordinary money could have covered, and the retirement-account room those dollars occupied is gone for good.
This is why the funding source belongs in the same conversation as when to run a Roth conversion: a conversion sized to your bracket but funded out of the account itself is smaller than the form suggests, and the shortfall compounds as long as the Roth stays invested.
What Withholding From the Conversion Actually Costs
The mechanics are easy to miss. If you convert $100,000 and instruct the custodian to withhold 24% for federal tax, $24,000 goes to the IRS and $76,000 arrives in the Roth.
| Funding Method | Amount Converted | Amount Reaching the Roth |
|---|---|---|
| Withhold 24% from the IRA | $100,000 | $76,000 |
| Pay tax from outside cash | $100,000 | $100,000 |
You reported and paid tax on the full $100,000, but only $76,000 is positioned to grow tax-free from that point forward. Convert the same $100,000 and pay the $24,000 from a savings account instead, and the full $100,000 lands in the Roth while your outside cash absorbs the bill. Same tax return, same year, meaningfully different Roth balance.
Hypothetical example for illustration only. Results are not guaranteed and depend on individual circumstances.
The gap isn't just the $24,000. It's the $24,000 plus whatever it would have earned inside a Roth over the decades that follow.
The gap isn't just the $24,000. It's the $24,000 plus whatever it would have earned inside a Roth over the decades that follow, none of it taxed on withdrawal under current law. That part never appears on the conversion confirmation, which is why it ranks alongside the common Roth conversion misconceptions as something to catch early.
The example leaves out two things. State tax rides along: Kansas and Missouri both tax IRA distributions, Kansas at 5.58% on joint income above $46,000 and Missouri at a 4.7% top rate for the 2025 and 2026 tax years. And if the money starts in a 401(k) rather than an IRA, withholding isn't elective. IRS Publication 590-A is explicit: when an eligible rollover distribution is paid directly to you, the plan must withhold 20%, and you can't waive it. The fix for plan money is the direct rollover, which moves the balance straight to the Roth IRA with nothing withheld.
Under 59 and a Half, Withholding Adds a Penalty
Amounts withheld from an IRA for taxes aren't converted, they're distributed to the IRS on your behalf. For someone under 59 and a half, that distributed portion is generally subject to the 10% early distribution penalty on top of ordinary income tax, unless an exception applies.
A saver in their mid-50s who withholds pays income tax on the full amount, loses those dollars from the retirement system, and pays a penalty on the very dollars that covered the tax.
Converted dollars also start their own five-year clock, running from January 1 of the conversion year, and under 59 and a half it governs that same 10% penalty on the taxable portion converted. Earnings are a separate test: tax-free only in a qualified distribution. Both clocks appear in the Roth IRA withdrawal rules.
That penalty exposure argues for having outside cash ready, or for converting less this year and revisiting next year, which is worth weighing against what waiting to convert really costs.
And if tax has already been withheld, there's a remedy. You have 60 days. IRS Publication 590-A treats the withheld amount as part of the distribution and says you can make up the amount withheld with funds from other sources. Replace those dollars out of pocket, roll the full pre-withholding amount into the Roth inside 60 days, and both the shortfall and the penalty exposure go away. The once-per-12-months rollover limit doesn't block it: Publication 590-A says conversions from traditional IRAs to Roth IRAs are not limited. What you can't undo is the conversion itself. Recharacterization was eliminated for conversions made after 2017, so the decision to convert is final even when the funding mistake is fixable.
Funding the Tax Bill Without Shrinking the Conversion
Size the conversion to the cash you can comfortably part with, not the other way around. Consider a saver who could cover the tax on a $60,000 conversion from outside funds but not the tax on a $100,000 one.
The smaller conversion arrives in the Roth intact. The larger one would have to fund its own tax bill out of the dollars being converted, so what ends up growing tax-free isn't the amount on the form. Which size makes sense depends on the household's full tax picture.
Hypothetical example for illustration only. Results are not guaranteed and depend on individual circumstances.
Selling from a taxable brokerage account to raise the cash works too, though the capital gains land in the same year's income, so plan the sale and the conversion together.
Timing the payment matters too. Withheld federal tax is generally treated as paid evenly across the year, while estimated payments count when you make them, so a late-year conversion funded by outside cash may call for an estimated payment or a withholding adjustment to stay inside the safe harbor rules.
The tax you can fund, the bracket you're filling, Medicare surcharges, Social Security taxation, and the years before required distributions all define the windows when conversions work best. Thresholds and surcharge tiers change, so confirm the numbers for the year you convert.
Should I pay Roth conversion taxes from the IRA or from cash?
Paying from cash or a taxable account is generally preferred: the entire converted amount reaches the Roth, where future growth is not taxed under current rules. Withholding settles the same bill with dollars that would otherwise have stayed in a tax-advantaged account.
What happens if I withhold taxes from a Roth conversion before 59 and a half?
The withheld portion is generally treated as a distribution rather than a conversion, so it is typically subject to the 10% early distribution penalty in addition to ordinary income tax unless an exception applies, which makes withholding notably more expensive under that age.
What if I do not have cash available to pay the conversion tax?
Converting a smaller amount your cash can cover is usually the better answer. A conversion is not all-or-nothing, and a series of smaller conversions funded from outside money accomplishes the same goal over several years.
Can I undo a Roth conversion if the tax bill is larger than expected?
Not the conversion itself. The ability to recharacterize was eliminated for conversions made after 2017, so the converted amount is fixed. The funding is not: if tax was withheld, IRS Publication 590-A lets you make up the withheld amount from other sources and roll the full pre-withholding amount into the Roth within 60 days, which restores the conversion to its intended size and removes the penalty exposure on the withheld portion.
Get the Funding Source Right Before You Convert
The conversion decision gets the attention. The funding decision is what actually determines how much of it ends up growing tax-free.
If you're planning a conversion, see how a coordinated Roth conversion strategy works, so the funding source and the timing get decided together.
This content is for educational purposes only and is not investment, tax, or legal advice.
